An email has now been sent by DigiCert to the provided email address:
It contains a link you need to click on to be able to generate your certificate.

Going to the provided link, you will need to check the box "I agree to the terms of the subscriber agreement", and then the button "Generate Certificate" on the bottom of the page;

After a second, you get a message saying that your certificate has been generated; your certificate is installed in your brower's certificates repository (see further section to see how to get it and use in your email client.